1. Field of the Invention
The present invention relates to a deformable mirror the curvature of which can be changed continuously and, more particularly, to a compact deformable mirror to which the semiconductor technique is applied.
2. Description of the Related Art
In recent years, a deformable mirror, which uses the Micro Electro-mechanical Systems technique, attracts attention. For example, a deformable mirror disclosed in Jpn. Pat. Applin. KOKAI Publication No. 2-101402 is an example of a deformable mirror. In this deformable mirror, as shown in FIG. 32, an electrode layer 3 is formed on a semiconductor substrate 1 through an insulating thin film 2. The semiconductor substrate 1 has a cavity 4 that allows central portions 5 of the insulating thin film 2 and electrode layer 3 to displace in the direction of thickness. An electrode layer 7 is formed on the bottom surface of the cavity 4 through an insulating thin film 6. The electrode layers 3 and 7 constitute a pair of opposing electrodes. The electrode layer 3 also serves as a reflection surface. The reflection surface is deformed into a concave by an electro-static force generated upon application of a voltage to the electrode layers 3 and 7.
The application range of the deformable mirror that uses the Micro Electro-mechanical Systems technique is widening, so the deformable mirror will be employed in various types of optical systems. According to one application, a reflection mirror portion is to be largely deformed to a degree that is not available conventionally.